1. Field of the Invention
The present invention relates to content addressable memory, and more specifically to encoding techniques for storing and searching data in content addressable memory utilizing resistive memory elements.
2. Description of Background
Content addressable memory (CAM) is a type of computer memory utilized in high speed searching applications. Most CAM devices utilize transistors configured as static random access memory (SRAM), and additional transistor circuits for match operations. Typically in these CAM devices search line access transistors and word line access transistors are necessary to operate and program individual memory cells in the memory arrays. The search line access transistors and word line access transistors are often comprised of power intensive large drive field effect transistors (FET).
Phase change material can also be utilized to store information in CAM devices. Phase change materials can be manipulated into different phases or states, with each phase representing a different data value. Generally, each phase exhibits different electrical properties. The amorphous and crystalline phases are typically two phases used for binary data storage (1's and 0's) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase.
One difficulty in using resistive memory elements, such as phase change memory, in CAM designs is the small sense margin when large data words are stored and searched in CAM. A single mismatching bit between a stored data word and a search word may not cause sufficient match current deviation to be detected. Conventional CAM designs with resistive memory cells are thus limited in the number of bits per stored word. The present invention addresses this limitation and other shortcomings of CAMs employing resistive memory elements.